I. Field of the Invention
The present invention relates to communications systems. More particularly, the present invention relates to a method and apparatus for identifying subscriber units in a wireless communication network.
II. Description of the Related Art
Wireless communications systems require the identity of subscribers (or subscriber units, such as wireless telephones, terminals, modems, etc.) to be determined for a number of purposes, including authentication for billing and to maintain secure communications over the connection between the subscriber unit and the party to which the subscriber is attempting to communicate. An electronic serial number (ESN) is a unique 32-bit serial number permanently stored in the subscriber unit equipment by the manufacturer. The ESN uniquely identifies a subscriber unit. The circuitry within the subscriber unit that provides the ESN is usually isolated from fraudulent contact or tampering. Many subscriber units are manufactured such that an attempt to alter the ESN renders the subscriber unit inoperative.
FIG. 1 illustrates the content of an ESN. The ESN 100 consists of a manufacturer""s code field 102 and serial number field 104. The serial number field is twenty-four bits long and designates a serial number 104 uniquely assigned to a particular subscriber unit. The manufacturer""s code field is eight bits in length and designates a manufacturer""s code uniquely assigned to each manufacturer of subscriber units. The Federal Communications Commission (FCC) has mandated that each subscriber unit be assigned an ESN, so that radio transmissions can be identified, if need be. In combination with the ESN, a mobile identification number (MIN) uniquely identifies a subscriber. The unique combination of the ESN and the MIN is used to register and qualify a subscriber for service. In addition, this combination is used to enable all network functions pertaining to an individual subscriber.
The Telecommunications Industry Association (TIA) standard TIA/EIA IS-41, entitled Cellular Radio Telecommunications Intersystem Operations, provides a standard for intersystem operations among mobile switching centers (MSCs), home location registers (HLRs), visitor location registers (VLRs) for cellular networks to support subscriber mobility. In IS-41, a unique subscriber identification is provided by concatenating the MIN and the ESN. This combination is used primarily for registration and authentication functions.
In code division multiple access (CDMA) systems, as standardized by the TIA in TIA/EIA IS-95-A, entitled Subscriber unit-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System, the electronic serial number is used to set the initial state of the scrambling pseudonoise (PN) generator. In IS-95-A, a 42-bit mask is generated in accordance with the 32-bit ESN. The first ten bits are a fixed sequence and the remaining 32 bits are a predetermined permutation of the subscriber unit ESN. The use of the ESN to provide a mask for the long code is described in U.S. Pat. No. 5,103,459, entitled xe2x80x9cSYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEMxe2x80x9d.
In addition, the ESN is used in authentication procedures as specified in TIA/EIA IS-41 (hereafter IS-41). Authentication is a set of functions used to prevent fraudulent access to cellular networks by phone illegally programmed with counterfeit mobile identification number (MIN) and electronic serial number (ESN) information. The functions require no subscriber intervention and provide a robust method of validating the true identity of a subscriber.
The authentication procedure specified in IS-41 is performed in accordance with the performance of a set of calculations, collectively known as the CAVE (cellular authentication and voice encryption) algorithm. The CAVE algorithm is described in U.S. Pat. No. 5,159,634, entitled xe2x80x9cCRYPTOSYTEM FOR CELLULAR TELEPHONYxe2x80x9d. The authentication process and algorithm are based upon two secret numbers: the authentication key (A-key) and shared secret data (SSD). The A-key is a 64-bit secret number that is a permanently stored in the subscriber unit and securely stored in the authentication center. The A-key is never transmitted over the air, but is used in the generation of the SSD. The SSD is result of a calculation using the A-key, the ESN and a random number shared between the subscriber unit and the network. It is by matching the generated SSD of the network with the generated SSD of the subscriber unit that authentication is performed.
With the number of subscriber units increasing dramatically, there is a need for electronic serial numbers beyond the number provided for using the current numbering scheme. In response to this need, a 56 bit extended electronic serial number (EESN) has been proposed. FIG. 2 illustrates the organization and content of the proposed EESN. As shown in FIG. 2, the EESN 200 has an eight-bit manufacturer""s code field 202 that indicates that an EESN is being used. The proposed method would require that a predetermined value be placed in the manufacturer""s code field of the EESN 200. One proposal is to have this predetermined value be equal to 128 decimal. The EESN also has a twenty-four-bit serial number field 204 that designates the serial number assigned to the subscriber unit. An eight-bit reserved field 206 provides additional capacity for expanding the current fields or adding an additional field at a later time. A sixteen-bit extended manufacturer""s field 208 designates the manufacturer""s code in the EESN. It can be seen that there are an additional eight bits provided in the EESN to designate the manufacturer""s code.
However, as described above, many existing operations require a 32 bit ESN. Thus, there is a need felt in the art for a method by which a 56 bit EESN can be used in the authentication, registration and scrambling operations that are to be performed using a 32 bit ESN.
Therefore, there is a need for a method and apparatus that can make wireless infrastructure that is designed to accommodate 32-bit ESNs compatible with newer subscriber units that are assigned a 56-bit EESN.
The method and apparatus disclosed herein generates a 32 bit digital xe2x80x9camended electronic serial numberxe2x80x9d (AESN) from a 56 bit xe2x80x9cextended electronic serial numberxe2x80x9d (EESN). The AESN distinguishes each subscriber unit within a wireless system from each other subscriber unit. Two distinct methods are disclosed. In accordance with the both the first and second method, an AESN is only generated when an EESN has been assigned to the subscriber unit by the manufacturer.
In accordance with the first method, a portion of the EESN referred to as the manufacturers code field (xe2x80x9cMFRxe2x80x9d) is tested to determine whether the subscriber unit has, in fact, been assigned an EESN. If the MFR value (i.e., the value designated in the MFR field) is equal to 128 decimal (xe2x80x9c1000 0000xe2x80x9d binary), then an EESN is being used. If so, then the least significant 8 bits of a portion of the EESN, referred to commonly as the extended manufacturer""s code field (xe2x80x9cEMFRxe2x80x9d) is appended to the 24 bits of the EESN that are commonly referred to as the xe2x80x9cserial numberxe2x80x9d field (xe2x80x9cSNxe2x80x9d). Accordingly, the AESN would comprise the 8 least significant bits of the EMFR and the 24 bits of the SN.
In accordance with the second method, each manufacturer would be required to generate, by applying a pseudo-random sequence, the 24 bit serial numbers which must be assigned to subscriber units that are produced by that manufacturer. The xe2x80x9cseedxe2x80x9d for the pseudo-random sequence is based on the manufacturer""s EMFR, and therefore different for each manufacturer. This serial number is then combined with the 8 bit MFR to generate an AESN whether the manufacturer has assigned an EESN or an ESN. That is, the 8 bits of the MFR taken together with the 24 bits of the serial number to comprise an AESN whether the manufacturer has assigned an EESN or an ESN.
The first method has the lowest probability that two subscriber units operating within the same region or metropolitan trading area will be assigned the same 32 bit value. However, the second method is simpler and is requires less adaptation by existing equipment within the wireless infrastructure.